Hydroformylation catalysts based on a binuclear rhodium complex are known, more particularly catalytic species of the type: ##STR2## are described in the U.S. Pat. No. 3,501,531.
Such catalysts, although giving good results, present the disadvantage of being comparatively inactive which necessitates extremely long reaction times or the use of high concentrations of catalyst which have the disadvantage of being costly. On the other hand, the application of high temperatures, which might reduce the reaction times, leads to a loss in the selectivity for obtaining the aldehyde due to the hydrogenation of the aldehydes into alcohols.